This invention relates to a motor control device for a vehicular power mirror, which is used to vary the number of rotations of a driving motor incorporated in a power mirror, such as a door mirror and a fender mirror, for a vehicle.
In general, the power mirror such as a door mirror and a fender mirror for a vehicle includes two driving motors for adjustment of mirror surface orientation: a vertical motion motor tilts a mirror surface up and down; a lateral motion motor tilts the mirror surface left and right.
One example of control devices for the above vehicular power mirror is disclosed in Japanese Laid-Open Patent Application, Publication No. 2001-138812 (the applicant of which is the assignee of the instant application), in which control is exercised utilizing the number of rotations of a driving motor. In this disclosure, a direct current brush motor is adapted for the driving motor. This control device includes a driving motor, a motor signal detector, and a pulse signal counter. In the motor signal detector, a pickup coil connected in series with the driving motor detects high-frequency motor brush switching signals generated from the driving motor, and the motor signal detector outputs thus-detected high-frequency motor brush switching signals shaped in a waveform of pulse signals. The pulse signal counter counts the pulse signals output from the motor signal detector.
According to the control device as above, if the signal level of the motor brush switching signals generated from the driving motor is low due to wear of the brush or a defective condition of the brush contact in the driving motor, dropouts or omission of the pulse signals could possibly take place because the motor brush switching signals could not accurately be shaped into the waveform of pulse signals. In this instance, accurate control could not be exercised over the number of rotations of the driving motor, to the extent that adjustment accuracy of the mirror surface orientation would disadvantageously deteriorate.
The present invention has been made in order to address the above disadvantages, and it is an exemplary general object of the present invention to provide a motor control device for a vehicular power mirror, in which accurate control can be exercised over the number of rotations of a driving motor even under conditions where the signal level of motor brush switching signals generated from the driving motor is low for various reasons.